1. Field of the Invention
The present invention relates to an electric brake that converts rotational motions of motors fixed to a brake system into linear motions so as to move forward pistons of the brake system and to press friction members to a rotary member to apply the brake.
2. Related Art
An internal combustion engine, which uses gasoline or the like as fuel, has been used as a power source in a vehicle such as an automobile to obtain high power. However, an electric vehicle or a hybrid electric vehicle has been used in recent years in terms of environmental measures or fuel efficiency, and an electric motor has been used as a main power source or an auxiliary power source. Accordingly, an electric brake has also been commonly used, in which an electric motor being supplied with electric power is used as a power source of braking. In general, the electric brake using an electric motor as a power source converts the rotational motion of the motor into a linear motion so as to move forward pistons of a brake system so that friction members are pressed to a rotary member to apply the brake. Therefore, when the rotation angle of the electric motor is analyzed, it is possible to control a pressing force (that is, displacement) that is applied to a brake rotor by a friction member through a displacement of the piston converted into a linear motion.
In general, a friction member is pressed to the rotary member such as a brake rotor, by a piston during the braking. However, when the friction member is pressed to the rotary member by the piston or the like, a pressure plate provided on the backside of the brake pad forming the friction member is pressed at a pin point. Accordingly, the pressure plate may be bent. As a result, since the brake pad is not uniformly contacted with the rotary member such as a brake rotor, there has been an undesirable possibility that an uneven wear occurs in the brake pad or the brake rotor. For this reason, a technology for preventing the uneven wear of the brake pad and the like has bee proposed (for example, see JP-A-2000-074106).
An electric brake system disclosed in JP-A-2000-074106 will be described in brief with reference to FIGS. 4A and 4B. A pressure plate 78 formed integrally with a brake pad 74 is formed so that a contact surface of the pressure plate to be contacted with a spindle 72 forms a convex part 78a. Further, the convex part 78a is formed to include a spherical large curvature part 78b at a contact portion to be contacted with the spindle 72, and a small curvature part 78c having a smaller curvature than the large curvature part 78b at a portion except for the contact portion. The pressure plate 78 may be fixed to a mounting bracket so that the center of the large curvature part 78b is on the axis of the spindle 72.
According to the above structure, when the bend of the brake pad in a pressing direction is suppressed in the electric brake system that uses an electric motor as a power source to obtain a braking force, it is possible to prevent the uneven wear of the brake pad 74. However, even though it is possible to suppress the uneven wear of the brake pad 74 caused by the pressure plate 78 in the pressing direction, any consideration is not made for a winding load generated when the brake pad 74 is pressed to a brake rotor 42, among common loads. For this reason, it has been still insufficient to reliably prevent the uneven wear of the brake pad.